Blood pressure and gastric motor responses to bradykinin and hydrochloric acid injected into somatic or visceral tissues.

Abstract

Both visceral and somatic nociceptive stimuli elicit reflex changes in blood pressure and gastric motor activity, but the exact type of response varies with the type of nociceptive stimulus and its site of application. Therefore, the present study compared the effects of visceral (i.p. or i.a.) and somatic (s.c.) administration of bradykinin and HCl on both mean arterial blood pressure (MAP) and intragastric pressure in anaesthetized rats. The nervous pathways mediating these responses were investigated by surgical or pharmacological inhibition of the possible reflex arcs. Bradykinin (i.a.--into the aortic arch, i.p., and s.c.), and HCl (i.p. and s.c.), elicited a fall in MAP followed by a transient increase. Intragastric pressure decreased in response to administration of these chemicals. Acute coeliac ganglionectomy reduced the gastric relaxations in response to both bradykinin and HCl, whereas vagotomy reduced only the gastric relaxations induced by HCl. Neither lesion influenced the changes in MAP after either chemical. Ablation of small diameter afferents by capsaicin or chemical sympathectomy by guanethidine reduced the changes in MAP after both chemicals, except that which occurred after i.a. injection of bradykinin. The secondary increase in MAP after i.a. and i.p. administration of algesics was increased after guanethidine. Both pretreatments reduced gastric relaxations in response to either chemical. Pretreatment of the rats with the bradykinin antagonist Hoe-140 reduced the responses to bradykinin but not to HCl. The results show that both visceral and somatic administration of painful chemicals elicit reflex falls in MAP and intragastric pressure.(ABSTRACT TRUNCATED AT 250 WORDS)